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    <title>Document</title>
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    <script>
        var arr = [1,2,3,4,5,7] //[1,2,7]
        arr.splice(2,3)
        console.log(arr);

        var arr = [1,2,3,4,5,7] //[1,8,9,7]
        arr.splice(1,4,8,9)
        console.log(arr);


        /* ==运算 */
        // Number(""),Number(" "),Number(null) => 输出 0
        console.log(false == ""); // true
        console.log(true == 1); // true
        console.log(null == undefined);  // true
        console.log(undefined == false);  // false
        console.log(1 == "1"); // true
        /* 1.只有有一边为 boolean 先两边转为number 
           2.一边为string，一边为number，先将两遍转为number
           
           // 两边都先转为number
           3. null == undefined
           4. null 和 undefined 不能转化为其他值
        */
    </script>
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